Transformer cooling means



Aug. 2, 1955 E. J. DIEBOLD TRANSFORMER COOLING MEANS Filed March 29,1951 3 Sheets-Sheet l INVENTO fog/440 JUI/IV eaao 2, 1955 E. J. DYIEBOLD2,714,709

TRANSFORMER COOLING MEANS Filed March 29, 1951 3 Sheets-Sheet 2ATTORNEYS Aug. 2, 1955 E. J. DIEBOLD TRANSFORMER COOLING MEANS 3SheetsSheet 3 Filed March 29, 1951 INVENTOR. Eva/#4 0 Ja/nvD/EB an! M4 wAM United States Patent Office TRANSFORMER COOLING MEANS Edward JohnDieboltl, Ardmore, Pa., assignor to I-T-E Circuit Breaker Company,Philadelphia, Pa., :1 corporation of Pennsylvania Application March 29,1951, Serial No. 218,115

1 Clair (Cl. 33661) My present invention relates to cooling means andmore particularly it relates to transformer cooling means that producecooling by a combination of heat conduction, convection and radiation.

It is wellknown to persons familiar in the art that the output of anypiece of electrical apparatus, i. e., generators, motors, transformers,etc. is limited by the rise in temperature caused by its losses. One ofthe most important problems is to provide some satisfactory means ofcooling said equipment. In transformers the losses are mainly theso-called copper losses and core losses. When a current flows in aconductor, it carries an irreversible transfer of energy, in the form ofheat, to the ambient surrounding the conductor. This irreversibletransfer of energy is what constitutes the socalled copper losses andvaries as the square of the current flowing in the conductor.

In transformers, copper losses are produced in the primary and secondarywinding and vary as the square of their respective currents. The corelosses are caused by the variation of the flux in the iron core anddepend upon the frequency, the maximum value of the flux wave, thequality of the iron, the thickness of the lamination and the volume orweight of the core.

These losses vary almost as the volume while the amount of heat that canbe dissipated depends upon the surface exposed.

More particularly, heat can be transferred in three different ways, thatis, by conduction, convection and radiation.

Heat is transmitted by conduction when heat energy diffuses graduallythrough a mass of matter passing from particle to particle from thenewer toward the older parts of a body.

Heat is transmitted by convection when heat is carried along by themotion of a stream of gas or liquid.

Heat is transmitted by radiation when heat energy is transmitted bywaves.

The coils of most transformers are placed, therefore, in oil containedin cast iron or sheet steel tanks. To en sure effective cooling, thecoil and core are so arranged that the heated oil may rise readily tothe top through ducts between the coil and between the coils and thecore. It will then pass down along the colder walls of the transformercore.

As only about one watt can be radiated from each 150 square inches ofdry surface of ordinary transformer cases with smooth sides, for eachdegree centigrade rise in temperature, special means for cooling have tobe provided except for the smallest transformers. Sufficient radiatingsurface can be obtained to keep transformers up to a few hundreds kws.cool by corrugating the sides of the cases. Corrugating or ribbing thesides of the cases increases the amount of heat radiated by about fiftyper cent.

When cooling water is available, the most common means of keeping largetransformers cool is to circulate water through coils of pipe placed inthe tops of transformer cases in the oil above the windings. When thisis done, corrugated containing cases are not necessary. Transformers forlow voltage, i. e., not over a few thousand volts, may be air cooled.

In this case, no oil is used, but air is circulated through the coil bymeans of a blower. In many cases, or, for example, in unattendedsub-stations, it is not possible to use artificial means of cooling.Under these conditions, special cases with very large radiating surfacesare used. The required increase in surface may be obtained by weldingvertical tubes to the cases at the top and bottom.

In later types of cases for large self-cooled transformers radiatingfins through which the oil can circulate are attached to the cases.Self-cooled transformers may be made, up to quite a few thousand kws. bythe use of such devices.

My novel invention provides means for cooling a transformer byconduction, convection and radiation.

More specifically, my novel invention provides means for carrying awayheat (copper losses) from the primary and secondary winding of atransformer by conduction and for dissipating said heat in thesurrounding air or oil by convection and radiation, thus increasing thekva. of a transformer using these novel cooling means.

If further cooling is necessary, my novel invention pro vides means forusing forced air or fluid circulation.

The main object of my present invention, therefore, is the provision ofmeans for cooling transformer windings by conduction, convection andradiation.

Another object of my invention is the provision of means whereby thecooling means also insulates one winding layer from the other.

A further object of my invention is the provision of means whereby thesecooling means can be easily mounted on the transformer coil.

Another object of my invention is the provision of means whereby thecooling effect can be easily increased by using forced air or fluidcirculation.

These and other objects of my invention will become apparent in thefollowing description and drawings in which:

Figure 1 is the plan view of an embodiment of my invention.

Figure 2 is the front view of a 13 kva. 230/ 4-5.5 volts transformerusing the cooling means of my invention.

Figure 3 is a side view partly in section of the transformer shown inFigure 2.

Figure 4 is a plan view of a transformer coil shown in Figure 2 takenfrom line 4-4 of Figure 3 looking in the direction of the arrows,showing one layer of a six-turn two-layer coil.

Figure 5 is a plan view of a transformer coil shown in Figure 2 takenfrom line 55 of Figure 2 looking in the direction of the arrows showingone layer of an eightturn two-layer coil.

Figure 6 is the front view of a 30 kva. 260/101.7 volts transformerusing the cooling means of my invention.

Figure 7 is a side view partly in section of the transformer shown inFigure 6.

Figure 8 is a cross-sectional view of the transformer shown in Figure 6taken from line 8-8 of Figure 7 looking in the direction of the arrows.

Figure 9 is a cross-sectional view of the transformer shown in Figure 6taken from line 9 of Figure 6 looking in the direction of the arrows.

Referring first to Figure 1 showing the transformer cooling means of myinvention, the cooling means 10 are made of a good heat conductingmetal, like aluminum, and are so shaped that the cooling surfaces 11between windings and cooling fins and the cooling surfaces 12 betweencooling fins and air are very long and permit a good transmission ofheat. The cross-section of fin 10 can be made 3 small because the heatconducting capacity of metals like aluminum is high.

In the particular embodiment of my invention shown in Figure 1, thecooling fins have a circular recess 13 so that fins 10 can easily beplaced around the tube 15. Because of opening 14, the cooling fins coveronly about three-quarters of the circumference, the remaining quarterbeing used for winding connection or being later filled by an insulationsp'acer 16 as shown in Figure 1. Opening 14 also cuts the eddy currentpath so that no eddy cu rent loss is produced by the presence of thecooling fins it In order to ensure good electric insulation whileproviding passage for the heat, each fin 10 is covered by a layer ofinsulating material, like glass cloth, which is later impregnated withinsulating varnish.

Referring now to Figures 2, 3, 4 and 5, showing a l3 kva. 230/455 voltstransformer having the cooling fins of my invention, the coils 20 arecentered by a tube 21 made of insulating material having sufficientmechanical strength to support coils 20, for example, Bakelite. Thecoils 20 comprise the primary winding and the secondary winding 49. Bothwindings are copper wires wound into flat pancake spools and are stackedalternatively on tube 21 with cooling fin 10 between each winding and apressboard insulation 41 between each coil layer of the same winding.

More specifically, tube 21 is first surrounded by pressboard insulation45, 46 of different thickness. Then the primary coils 30 and secondarycoils are placed around insulation 45, 46 of tube 21. All coils 30 and40 are wound with cotton insulated square wire and in this particularembodiment the coils are as follows: The first coil 52 is a six-turncoil in two layers of three turns p'er layer as shown in Figure 4; thenext nine coils 53 are eight-turn coils in two layers of four turns perlayer as shown in Figure 5; then one four tap primary coil 54; folowedby eight coils 55 of eight turns in two layers of four turns per layer;next two half coils secondary 56 having each four turns; then one eightturn coil 57 in two layers of four turns per layer and finally onefour-turn coil 58.

The coils constituting the primary winding 30 are connected togetherthrough soldered connections 59, while the coils constituting thesecondary winding 49 are connected together through similar solderedconnections 60.

As previously mentioned, each coil is separated from the previous andthe next by a thin sheet of pressboard insulation 41, while cooling fins10 are placed between coil layers.

A thicker cooling fin 61 can also be placed between appropriate layersof coils 62, 63. The heat then follows this path: from the windings ofcoils 52, 53, etc. to the surfaces 11 of cooling fins 10 by conduction,from surfaces 12 of cooling fins 10 to ambient air by convection andradiation.

Since fins 10 are made of good heat-conducting material after arelatively short period of operation, their temperature attempts toreach the average temperature of the windings 52, 53 etc. but since theambient air or oil is at a lower temperature and a large section 12 ofcooling fins 10 is immersed in this ambient air or oil, the temperatureof the cooling fins 10 will not reach the average temperature of thewindings 52, 53 etc. but will remain at a point of equilibriumcorresponding to a temperature between the average temperature of thewindings 52, 53, etc. and that of the ambient. The temperature gradientis directed from the windings 52, 53, etc. to the cooling fins 10 in adirection approximately perpendicular to the fins 10. In the fins 19 itis directed outwardly from the tube 21 and in section 12 of fins 10 itis directed perpendicularly to the surfaces of the cooling fins 10.

If more cooling is needed, heat can be taken away from the fins 10 morerapidly by blowing air on the fins 10 by means of a fan.

Referring finally to Figures 6, 7, 8, 9 showing a 30 kva. 260/l0l.7 volttransformer having the cooling fins of my invention, the coils 129 arecentered by a tube 121 made of insulating material having sufiicientmechanical strength to support coils 120, for example, Bakelite. Coilscomprise the primary winding 130 and the secondary winding 140. Bothwindings are copper wires wound into flat pancake spools and are stackedalternatively on tube 121: primary 130, cooling fin 14), secondary 140,cooling fin 10.

More specifically, tube 121 is first surrounded by pressboard insulation145, 146 of different thickness. The coils 120 comprising primarywinding 13% and secondary winding 1% are placed around pressboardinsulation 145, 146 of tube 121. And finally cooling fins 10 are placedbetween each layer of coil 120.

More specifically, fin 10 actually comprises three types of coolingfins; the first type 147 without sheet insulation is placed betweenlayers of the same coils, while the second type 148 with sheetinsulation 149 is placed between each coil. A thicker and heaviercooling fin 150 can also be placed between appropriate layers as betweenlayers 151 and 152. Here too the primary winding coils 130 are connectedto each other by soldered connections 153, while the secondary windingcoils are connected to each other by similar soldered connections 154.

From a comparison of the two embodiments of my invention above shown, itis easily seen that the number of fins 10 in the second embodiment(Figures 6, 7, 8, 9) is greater than in the first embodiment (Figures 2,3, 4, 5) because the kva. capacity of the second transformer is greaterthan in the first, that is, more heat is provided in the secondtransformer than in the first and hence more cooling is necessary.

For both embodiments the impregnation of the cooling fins 10 withinsulating varnish is made when the transformer is fully assembled andafter vacuum drying.

The finished transformer is mounted with the legs in a horizontalposition such that the cooling fins 10 lie in a vertical plane andpermit a free vertical flow of the air between them.

In the second embodiment the number of fins 18, 19 was increased withrespect to the first embodiment because the kva. capacity of the secondtransformer is greater than in the first, that is, more heat isgenerated in the second embodiment than in the first.

In the foregoing I have described my invention solely in connection withspecific illustrative embodiments thereof. Since many variations andmodifications of my invention will now be obvious to those skilled inthe art, I prefer to be bound not by the specific disclosures hereincontained but only by the appended claim.

I claim:

In a transformer comprising a cylindrical core, a plurality of primarycoils, a plurality of secondary coils, core insulation means, coilinsulation means and cooling fins; said core insulation means beingconcentric with said cylindrical core and positioned on the outerperipheral surface thereof, said plurality of primary and secondarycoils being positioned in concentric relation to said cylindrical coreand being positioned around the outer periphery of said core insulationmeans, said core insulation means insulating said cylindrical core fromsaid plurality of primary and secondary coils, each of said coilscomprising a plurality of layers of pancaked electrical conductingwindings, said coil insulation means being a pressboard insulation discpositioned between adjacent coils to electrically insulate each of saidplurality of coils from the other coils, said cooling fins comprising adiscontinuous aluminum disc, having a discontinuous sector therein topermit winding connections, said cooling fins being covered on bothsides by an insulating varnish impregnated glass 6 cloth, said coolingfins being located between adjacent 714,232 Pichler Nov. 25, 1902 coillayers around said core insulation. 1,159,770 Hyde Nov. 9, 19151,602,043 Pfiffner Oct. 5, 1926 References Cited in the file of thispatent 1,723,840 Burnham Aug. 6, 1929 UNITED STATES PATENTS 5 1,938,421Gilbert Dec. 5, 1933 591,869 Moody Oct. 19, 1897

